Garbage collection for objects within object store

ABSTRACT

Techniques are provided for managing objects within an object store. An object is maintained within an object store. The object is used to store data of a snapshot of a file system hosted by a remote computing device. A determination is made that the snapshot was deleted by the remote computing device. Bitmaps describing objects within the object store that are related to snapshots of the file system are evaluated to determine that the object is unique to the deleted snapshot. The object is freed from storage within the object store.

BACKGROUND

Many users utilize cloud computing environments to store data, hostapplications, etc. A client device may connect to a cloud computingenvironment in order to transmit data from the client device to thecloud computing environment for storage. The client device may alsoretrieve data from the cloud computing environment. In this way, thecloud computing environment can provide scalable low cost storage.

Some users and businesses may use or deploy their own primary storagesystems such as clustered networks of nodes (storage controllers) forstoring data, hosting applications, etc. A primary storage system mayprovide robust data storage and management features, such as datareplication, data deduplication, encryption, backup and restorefunctionality, snapshot creation and management functionality,incremental snapshot creation, etc. However, storage provided by suchprimary storage systems can be relatively more costly and less scalablecompared to cloud computing storage. Thus, cost savings and scalabilitycan be achieved by using a hybrid of primary storage systems and remotecloud computing storage. Unfortunately, the robust functionalityprovided by primary storage systems is not compatible with cloudcomputing storage, and thus these features are lost such as compressionand deduplication otherwise provided by a primary storage system.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in which an embodiment of the invention may be implemented.

FIG. 2 is a component block diagram illustrating an example data storagesystem in which an embodiment of the invention may be implemented.

FIG. 3 is a flow chart illustrating an example method for managingobjects within an object store, wherein metadata is attached to anobject header of an object.

FIG. 4 is a component block diagram illustrating an example system formanaging objects within an object store, wherein metadata is attached toan object header of an object.

FIG. 5 is a flow chart illustrating an example method for managingobjects within an object store, wherein garbage collection is performedfor the objects within the object store.

FIG. 6 is a component block diagram illustrating an example system formanaging objects within an object store, wherein garbage collection isperformed for the objects within the object store.

FIG. 7 is a flow chart illustrating an example method for managingobjects within an object store, wherein defragmentation is performed forthe objects within the object store.

FIG. 8 is a component block diagram illustrating an example system formanaging objects within an object store, wherein defragmentation isperformed for the objects within the object store.

FIG. 9 is an example of a computer readable medium in which anembodiment of the invention may be implemented.

FIG. 10 is a component block diagram illustrating an example computingenvironment in which an embodiment of the invention may be implemented.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

Many users want primary storage system services, such as datareplication, data deduplication, encryption, backup and restorefunctionality, snapshot creation and management functionality, etc. tobe compatible with cloud storage provided by a cloud storageenvironment. In an example, primary data accessed by client devices maybe stored within a primary storage system and secondary data (e.g.,replicated primary data and snapshot data) may be stored in the cloudstorage environment (e.g., an object store) in order to reduce anoverall total cost of ownership of the secondary data because cloudstorage is more cost effective than primary storage. However, manyprimary storage system services are incompatible with the cloud storageenvironment, and thus such features are unavailable.

Accordingly, methods and systems are provided herein that may providevarious primary storage system services for a cloud storage environmentin order to achieve efficient space and resource management, andflexible scaling in cloud. Additionally, this invention provides pseudoread only snapshots in cloud. Consumers of these snapshots may choose toderive just the logical data represented by these snapshots or canadditionally derive additional metadata associated with the logical dataif required. This additional metadata is created post snapshot creationand hence is not directly part of the logical view of the snapshot. Thepresent system provides flexible, scalable, and cost effectivetechniques for leveraging cloud storage for off-premises operations onsecondary data, such as analytics, development testing, virus scan, loaddistribution, etc. The present system provides the ability to modifycloud objects (e.g., a unit of storage within a cloud storageenvironment) without changing the meaning or accessibility of useabledata in the cloud objects (e.g., a cloud object comprising a snapshotcopy of primary data maintained in a primary storage system). Thepresent system provides the ability to modify cloud objects to addadditional metadata and information such as analytics data, virus scandata, etc. to useable data without modifying the useable data. Thus, acloud object is maintained as a pseudo read only object because in-usedata is unmodifiable while unused or freed data is modifiable such as bya defragmentation and/or garbage collection process to remove the freeddata.

The present system provides the ability to detect changes in cloudobjects in order to resolve what data of the cloud objects is thecorrect data. The present system provides the ability to performdefragmentation and garbage collection for cloud objects by a cloudservice hosted by the cloud storage environment. Defragmentation andgarbage collection are provided without affecting access to other in-usedata within cloud objects (e.g., in-use snapshot data stored within acloud object that is used by one or more applications at various remotecomputers). This allows for more true distributed and infinite scaledata management. The present system provides for the ability to runanalytics on cloud objects (e.g., read/write analytics of data access todata within a cloud object) using analytic applications hosted withinthe cloud storage environment. The analytics can be attached to cloudobjects even though the cloud objects are read only. The present systemprovides for deduplication of cloud objects. In this way, cloud objectscan be modified while still maintaining consistency of in-use datawithin the cloud objects (e.g., maintaining consistency of a file systemcaptured by a snapshot that is stored within a cloud object) and withoutcompromising a read only attribute of the cloud objects. Also,computationally expensive processes like garbage collection, analytics,and defragmentation are offloaded from on-premises primary storagesystems to cloud services within the cloud storage environment.

In one embodiment, objects within an object store (e.g., cloud objectswithin a cloud computing environment) can be maintained with a read onlyattribute such that data within objects can beoverwritten/modified/freed so long as in-use data within the objects isnot altered. In particular, an object may be maintained within an objectstore, such as a cloud computing environment. The object comprises aplurality of slots, such as 1024 or any other number of slots. Each slotis used to store a unit of data. The data within each slot is read-only.In particular, the data is read only when in-use, such as where one ormore applications are referencing or using the data (e.g., anapplication hosted by a remote computing device is storing data of asnapshot of a local file system within a slot of an object, and thus thesnapshot data is in-use until a particular event occurs such as theremote computing device deleting the snapshot). In an example, theobject comprises snapshot data of a file system, a volume, a logicalunit number (LUN), a file, or any other data of a remote computingdevice (a primary storage system). In this way, the object comprises aread only snapshot of data of the remote computing device. In oneexample, a plurality of objects corresponding to read only snapshots ofthe file system of the remote computing device are stored within theobject store. Each object is assigned a unique sequence identifier.

A first rule is enforced for the object. The first rule specifies thatin-use slots are non-modifiable and unused slots are modifiable. Anin-use slot is a slot that stores data actively referenced, used, and/ormaintained by a remote computing device (a primary storage system). Forexample, an in-use slot may be a slot that comprises snapshot data(e.g., secondary/replicated data) of a snapshot created by a remotecomputing device. The slot becomes an unused slot when the data is nolonger actively referenced, used, and/or maintained, such as where theremote computing device deletes the snapshot. Thus, if a slot is in-use,then the data within the slot cannot be modified. Otherwise, data inunused slots (e.g., stale data that is no longer referenced or used) canbe modified, such as deleted/freed by garbage collection functionalityor defragmentation functionality.

Additional information for the object may be generated. The additionalinformation may comprise analytics (e.g., read/write statistics ofaccess to the object), virus scan information, development testing data,and/or a variety of other information that can be generated for theobject and the data stored therein. In an example, the additional datais generated by a cloud service or application executing within thecloud computing environment. This will offload processing and resourceutilization that would otherwise be used by the remote computing device(primary storage system) to perform such analytics and processing.

Metadata of the additional information is attached to an object headerof the object. The object header is used to store metadata for each slotof the object. In one example, the metadata specifies a location of theadditional information within the object, such as a particular slot intowhich the additional information is stored. In another example, themetadata may comprise the additional information, and thus theadditional information is stored into the object header. The metadata isattached in a manner that does not change a meaning or accessibility ofuseable data within in-use slots of the object. In particular,applications that are allowed to merely access user data within theobject (e.g., the applications are unaware or have no reason to accessthe additional information) are provided with only access to the userdata and are not provided with access to the metadata or additionalinformation. Thus, these applications continue to access user datawithin the object in a normal manner. For application that are allowedto access both the user data and the additional information, thoseapplications are provided with access to the user data and the metadatafor identifying and accessing a location of the additional informationwithin the object. The first rule is enforced such that user data(in-use data) is retained in an unmodified state within the objectnotwithstanding the metadata and/or additional information beingassociated with the object.

In an example, a second rule is enforced for the object. The second rulespecifies that related read operations are to be directed to a sameversion of an object. For example, an object corresponds tosecondary/replicated snapshot data of a file system maintained by aremote computing device. Each time a new snapshot of the file system iscreated, a new version of the object is created to capture changes tothe file system. In another example, since in-use data within the objectis read only and unmodifiable, any modifications to slots with in-usedata will result in a new version of the object being created with themodified data.

If multiple read operations are related, then those read operationsshould be executed upon the same version of the object for dataconsistency purposes. This is achieved by comparing timestamp data ofthe related read operations. If the timestamp data between the relatedread operations is mismatched, then the related read operations areretried because the related read operations were executed upon differentversions of the same object. If the timestamp data between the readoperations matches, then the related read operations are consideredsuccessful. In an example, a first related read operation reads theobject header of the object to identify a slot from which data is to beread. A second related read operation is executed to read data from theslot. The two related read operations should be executed upon the sameversion of the object/slot (e.g., the operations can be executed upondifferent versions such as where data of a current version of the objectis modified between execution of the operations, thus creating a newversion of the object with the modified data since the object is readonly and the original data is unmodifiable within the current version ofthe object). Thus, timestamp data of the two related read operations isused to determine whether the two related read operations were executedupon the same version of the object/slot and thus should be consideredcomplete or should be retried.

In one embodiment, garbage collection is provided for objects within theobject store. The objects have a read only state, such that enforcementof the first rule ensures that in-use data within slots of an object isnot modifiable, thus making objects pseudo read only objects becauseonly unused slots can be modified/freed of unused data. In an example,an object is used to store data of a snapshot of a file system hosted bya remote computing device. The snapshot may be determined as beingdeleted by the remote computing device, and thus slots comprisingsnapshot data of the deleted snapshot are now considered to be unusedslots as opposed to in-use slots.

Each snapshot of the file system may be associated with a bitmap thatidentifies objects within the object store that correspond to aparticular snapshot. Thus, the bitmaps can be evaluated to identify whatobjects comprise data of particular snapshots. For example, a bitmap ofthe deleted snapshot can be used to identify the object and otherobjects as comprising data of the deleted snapshot.

A garbage collection operation is executed to free objects (e.g. freeunused data from unused slots) from the object store in order to reducestorage utilization of the object store that would otherwise beunnecessarily used to store stale/unused data. In an example, thegarbage collection operation is executed by a cloud service in order toconserve resource consumption by the remote computing device (primarystorage system) otherwise used to execute the garbage collectionoperation. The garbage collection operation free objects from the objectstore based upon the objects uniquely corresponding to deletedsnapshots. That is, if an object stores data of only deleted snapshotsand does not store data of active/undeleted snapshots, then the garbagecollection process can free/delete that object. For example, the bitmapsdescribing objects within the object store that are related to snapshotsof the file system are evaluated to determine whether the object isunique to the deleted snapshot and/or unique to only deleted snapshots(e.g., the object does not comprise data of active/undeleted snapshots).If so, then the object is freed from the object store. However, if theobject is not unique to only deleted snapshot(s) such as where theobject also stores data of an active/undeleted snapshot, then the objectis not freed.

In an embodiment, defragmentation is provided for fragmented objectswithin the object store. In an example, defragmentation is implementedby a cloud service or application executing in the object store in orderto conserve resources otherwise used by a remote computing device(primary storage system) that would execute defragmentationfunctionality. An object within the object store is determined to be afragmented object based upon the object comprising at least one freedslot from which data was freed. For example, a freed slot may comprisean unused slot comprising unused data no longer referenced/used by aremote computing device (e.g., data of a deleted snapshot). Accordingly,the fragmented object may comprise one or more in-use slots of in-usedata currently referenced/used by a remote computing device and one ormore freed slots of freed data (e.g., unused slots comprising unuseddata).

The fragmented object is compacted to retain the in-use data and excludethe freed data (the unused data) as a written object. Because compactingmay store the in-use data in new slots, an object header of the objectis updated with new locations of the in-use data within the rewrittenobject. In this way, defragmentation is performed for objects within theobject store.

As provided herein, an object file system is provided that is used tostore, retrieve, and manage objects within an object store, such as acloud computing environment. The object file system is capable ofrepresenting data in the object store in a structured format. It may beappreciated that any type of data (e.g., a file, a directory, an image,a storage virtual machine, a logical unit number (LUN), applicationdata, backup data, metadata, database data, a virtual machine disk,etc.) residing in any type of computing device (e.g., a computer, alaptop, a wearable device, a tablet, a storage controller, a node, anon-premise server, a virtual machine, another object store or cloudcomputing environment, a hybrid storage environment, data already storedwithin the object store, etc.) using any type of file system can bestored into objects for storage within the object store. This allows thedata to be represented as a file system so that the data of the objectscan be accessed and mounted on-demand by remote computing devices. Thisalso provides a high degree of flexibility in being able to access datafrom the object store, a cloud service, and/or a network file system foranalytics or data access on an on-demand basis. The object file systemis able to represent snapshots in the object store, and provides theability to access snapshot data universally for whomever has access toan object format of the object file system. Snapshots in the objectstore are self-representing, and the object file system provides accessto a complete snapshot copy without having to access other snapshots.

The object file system provides the ability to store any number ofsnapshots in the object store so that cold data (e.g., infrequentlyaccessed data) can be stored for long periods of time in a costeffective manner, such as in the cloud. The object file system storesdata within relatively larger objects to reduce cost. Representation ofdata in the object store is complete, such that all data and requiredcontainer properties can be independently recovered from the objectstore. The object file system format ensures that access is consistentand is not affected by eventual consistent nature of underlying cloudinfrastructure.

The object file system provides version neutrality. Changes to on-premmetadata versions provide little impact on the representation of data inthe object store. This allow data to be stored from multiple versions ofon-prem over time, and the ability to access data in the object storewithout much version management. The object file system provides anobject format that is conducive to garbage collection for freeingobjects (e.g., free slots and/or objects storing data of a deletesnapshot), such as where a lower granularity of data can be garbagecollected such as at a per snapshot deletion level.

In an embodiment, snapshots of data, such as of a primary volume,maintained by a computing device (e.g., a node, storage controller, orother on-prem device that is remote to the object store) can be createdby the computing device. The snapshots can be stored in the object storeindependent of the primary volume and can be retained for any durationof time. Data can be restored from the snapshots without dependency onthe primary volume. The snapshot copies in the object store can be usedfor load distribution, development testing, virus scans, analytics, etc.Because the snapshot copies (e.g., snapshot data stored within objects)are independent of the primary volume at the computing device, suchoperations can be performed without impacting performance of thecomputing device.

A snapshot is frozen in time representation of a filesystem. All thenecessary information may be organized as files. All the blocks of thefile system may be stitched together using cloud block numbers (e.g., acloud block number comprises a sequence number of an object and a slotnumber of a slot within that object) and the file will be represented bya data structure (e.g., represented in a tree format of a treestructure) when stored into the object store within one or more objects.Using cloud block numbers, a next node within the tree structure can beidentified for traversing the tree structure to locate a noderepresenting data to be accessed. The block of the data may be packedinto bigger objects to be cloud storage friendly, where blocks arestored into slots of a bigger object that is then stored within theobject store. All the indirections (pointers) to reach leaf nodes of afile (e.g., user data such as file data is represented by leaf nodeswithin the tree structure) may be normalized and may be versionindependent. Every snapshot may be a completely independent copy and anydata for a snapshot can be located by walking the object file system.While doing incremental snapshot copy, changed blocks between twosnapshots may be copied to the object store, and unchanged blocks willbe shared with previous snapshots as opposed to being redundantly storedin the object store. In this way, deduplication is provided for andbetween snapshot data stored within objects of the object store. As willbe described later, an embodiment of a snapshot file system in theobject store is illustrated by FIG. 4B.

Cloud block numbers are used to uniquely represent data (e.g., a block'sworth of information from the computing device) in the object store atany point in time. A cloud block number is used to derive an object name(e.g., a sequence number) and an index (a particular slot) within theobject. An object format, used by the object file system to formatobjects, allows for sharing of cloud blocks. This provides for storagespace efficiency across snapshots so that deduplication and compressionused by the computing device will be preserved. Additional compressionis applied before writing objects to the object store and information todecompress the data is kept in the object header.

Similar to data (e.g., a file, directory, or other data stored by thecomputing device), metadata can be stored into objects. Metadata isnormalized so that the restoration of data using the metadata from anobject to a remote computing device will be version independent. Thatis, snapshot data at the computing device can be stored into objects ina version neutral manner. Snapshots can be mounted and traversedindependent of one another, and thus data within an object isrepresented as a file system, such as according to the tree structure.The format of non-leaf nodes of the tree structure (e.g., indirects suchas pointers to other non-leaf nodes or to leaf nodes of user data) canchange over time. In this way, physical data is converted into a versionindependent format as part of normalization. Denormalization may beperformed while retrieving data from the objects, such as to restore asnapshot. In an example of normalization, a slot header in an object hasa flag that can be set to indicate that a slot comprises normalizedcontent. Each slot of the object is independently represented. Slot datamay comprise version data. The slot data may specify a number of entrieswithin the object and an entry size so that starting offsets of a nextentry can be calculated from the entry size of a current entry.

In an embodiment, denormalization of a first version of data/metadata(e.g., a prior version) can be retrieved from data backed up in anobject according to a second version (e.g., a future version). In anexample, if the future version added a new field, then duringdenormalization, the new field is skipped over. Denormalization of afuture version can be retrieved from data backed up in an objectaccording to a prior version. A version indicator in the slot data canbe used to determine how of an entry is to be read and interpreted, andany missing fields will be set to default values.

In an embodiment of the object format of objects stored within theobject store, relatively larger objects will be stored in the objectstore. As will be described later, an embodiment of an object isillustrated by FIG. 4C. An object comprises an object header followed bydata blocks (slots). The object header has a static array of slotcontext comprising information used to access data for slots. Each slotcan represent any length of logical data (e.g., a slot is a base unit ofdata of the object file system of the object store). Since data blocksfor metadata are normalized, a slot can represent any length of logicaldata. Data within the slots can be compressed into compression groups,and a slot will comprise enough information for how to decompress andreturn data of the slot.

In an embodiment, storage efficiency provided by the computing device ispreserved within the object store. A volume copied from the computingdevice into objects of the object store is maintained in the objectstore as an independent logical representation of the volume. Anygranularity of data can be represented, such as a directory, a qtree, afile, or other data container. A mapping metafile (a VMAP) is used tomap virtual block IDs/names (e.g., a virtual volume block number, ahash, a compression group name, or any other set of names of acollection of data used by the computing device) to cloud block numbersin the object store. This mapping metafile can be used to trackduplicate data per data container for storage efficiency.

The mapping metafile enables duplicate data detection of duplicate data,such as a duplicate block or a compression group (e.g., a compressedgroup of blocks/slots within an object). The mapping metafile is used topreserve sharing of data within and across multiple snapshots storedwithin objects in the object store. The mapping metafile is used forsharing of groups of data represented by a unique name. The mappingmetafile is used to populate indirect blocks with corresponding cloudblock numbers for children nodes (e.g., compressed or non-compressed).The mapping metafile is used to help a garbage collector make decisionson what cloud block numbers can be freed from the object store when acorresponding snapshot is deleted by the computing device. The mappingmetafile is updated during a snapshot copy operation to store snapshotdata from the computing device into objects within the object store. Anoverflow mapping metafile can also be used, such as to represent entrieswith base key collision. The overflow mapping metafile will supportvariable length key and payload in order to optimize a key sizeaccording to a type of entry in the overflow mapping metafile.

The mapping metafile may be indexed by virtual volume block numbers orstarting virtual volume block numbers of a compression group. An entrywithin the mapping metafile may comprise a virtual volume block numberas a key, a cloud block number, an indication of whether the cloud blocknumber is the start of a compression group, a compression indicator, anindicator as to whether additional information is stored in the overflowmapping metafile, a logical length of the compression group, a physicallength of the compression group, etc. Entries are removed/invalidatedfrom the mapping metafile if corresponding virtual volume block numbersare freed by the computing device, such as when a snapshot is deleted bythe computing device.

The data structure, such as the tree structure, is used to representdata within an object. Each node of the tree structure is represented bya cloud block number. The key to the tree structure may uniquelyidentify uncompressed virtual volume block numbers, a contiguous ornon-contiguous compression group represented by virtual volume blocknumbers associated with such, and/or an entry for non-starting virtualvolume block numbers of the compression group to a starting virtualvolume block number of the compression group. A key will comprise avirtual volume block number, a physical length of a compression group,an indicator as to whether the entry represents a start of thecompression group, and/or a variable length array of virtual volumeblock numbers of either non-starting virtual volume block numbers or thestarting virtual volume block number (if uncompressed then this is fieldis not used). The payload will comprise cloud block numbers and/or flagscorresponding to entries within the mapping metafile.

Before transferring objects to the object store for an incrementalsnapshot, the mapping metafile is processed to clear any stale entries.This is to ensure that a stale virtual volume block number orcompression group name is not reused for sharing (deduplication). Inparticular, between two snapshots, all virtual volume block numberstransitioning from a 1 to 0 (to indicate that the virtual volume blocknumbers are no longer used) in a snapshot to be copied to the objectstore in one or more objects are identified. Entries within the mappingmetafile for these virtual volume block numbers transitioning from a 1to 0 are removed from the mapping metafile. In this way, all entriesusing these virtual volume block numbers are invalidated.

As part of copying a snapshot to the object store, changed data andindirections for accessing the changed data are transferred (or all datafor initialization). In particular, changed user data of the computingdevice is traversed through buftrees using a snapdiff operation todetermine a data difference between two snapshots. Logical(uncompressed) data is read and populated into objects and associatedwith cloud block numbers. To preserve storage efficiency, a mapping froma unique name representing the logical data (e.g., virtual volume blocknumber or a compression group name for compressed data) to a cloud blocknumber (e.g., of a slot within which the logical data is stored) isrecorded in the mapping metafile. Lookups to the mapping metafile willbe performed to ensure only a single copy of changed blocks are copiedto the object store. Metadata is normalized for version independency andstored into objects. Indirects (non-leaf nodes) are stored in the objectto refer to unchanged old cloud blocks and changed new cloud blocks arestored in the object, which provides a complete view of user data andmetadata for each snapshot. Inodes are written to the object store whilepushing changed inofile blocks to the object store. Each inode entrywithin an inofile is normalized to represent a version independent inodeformat. Each inode will have a list of next level of indirect blocks(e.g., non-leaf nodes of the tree structure storing indirects/pointersto other nodes). Snapinfo objects comprise snapshot specificinformation. A snapinfo object of a snapshot has a pointer to a root ofa snapshot logical file system. A root object for each primary volume(e.g., a primary volume for which a snapshot is captured) is copied tothe object store. Each snapshot is associated with an object ID(sequence number) map that tracks which objects are in use in a snapshot(e.g., which objects comprise data of the snapshot) and is subsequentlyused for garbage collection in the future when a particular snapshot isdeleted.

In an embodiment of data access and restoration, the tree formatrepresents an object file system (a cloud file system) that can bemounted and/or traversed from any remote device utilizing APIs using athin layer orchestrating between client requests and object file systemtraversal. A remote device provides an entry point to the object treeusing a universal identifier (UUID) that is a common identifier for allobject names for a volume (or container). A rel root object is derivedfrom the UUID, which has pointers (names) to next level snapinfoobjects. If a user is browsing a snapshot, a snapshot snapinfo is lookedup within snapinfo objects. If no snapshot is provided, then latestsnapshot info is used. The snapshot info has cloud block numbers for aninode file. The inode file is read from the object store using the cloudblock number and an inode within the inode file is read by traversingthe inode file's tree structure. Each level including the inode has acloud block number for a next level until a leaf node (a level 0 blockof data) is read. Thus, the inode for the file of interest is obtained,and the file's tree structure is traversed by looking up cloud blocknumber for a next level of the tree structure (e.g., a cloud blocknumber from a level 1 is used to access the level 0 block) until therequired data is read. Object headers and higher level indirects arecached to reduce the amount of access to the object store. Additionally,more data may be read from the object store than needed to benefit fromlocality for caching. Data access can be used to restore a complete copyof a snapshot, part of a snapshot (e.g., a single file or directory), ormetadata.

In an embodiment of read/write cloning, a volume or file, backed from asnapshot in the object store, is created. Read access will use a dataaccess path through a tree structure. At a high level, write access willread the required data from the object store (e.g., user data and alllevels of the file/volume tree that are part of user data modificationby a write operation). The blocks are modified and the modified contentis rewritten to the object store.

In an embodiment, defragmentation is provided for objects comprisingsnapshot copies in the object store and to prevent fragmented objectsfrom being sent to the object store during backup. Defragmentation ofobjects involves rewriting an object with only used data, which mayexclude unused/freed data no longer used by the computing device (e.g.,data of a deleted snapshot no longer referenced by other snapshots). Anobject can only be overwritten if used data is not changed. Objectsequence numbers are not reused. Only unused data can be freed, but useddata cannot be overwritten. Reads will ensure that slot header and dataare read from same object (timestamp checking). Reading data from theobject store involves reading the header info and then reading theactual data. If these two reads go to different objects (as determinedby timestamp comparison), then the read operation is failed and retried.

Defragmentation occurs when snapshots are deleted and objects could notbe freed because another snapshot still contains some reference to theobjects that would be freed (not all slots within these objects arefreed but some still comprise used data from other snapshots). A slotwithin an object can only be freed when all snapshots referring to thatslot are deleted (e.g., an oldest snapshot having the object in use suchthat younger snapshots do not reuse the freed slots). Also, ownershipcount can be persistently stored. When a snapshot is deleted, allobjects uniquely owned by that snapshot are freed, but objects presentin other snapshots (e.g., a next/subsequent snapshot) are not freed. Acount of such objects is stored with a next snapshot so that the nextsnapshot becomes the owner of those objects. Defragmentation is onlyperformed when a number of used slots in an object (an object refcount)is less than a threshold. If the number is below a second threshold,then further defragmentation is not performed. In order to identify usedslots and free slots, the file system in the snapshot is traversed and abitmap is constructed where a bit will be used to denote if a cloudblock is in use (a cloud block in-use bitmap). This map is used tocalculate the object refcount.

To perform defragmentation, the cloud block in-use map is prepared bywalking the cloud snapshot file system. This bitmap is walked togenerate an object refcount for the object. The object refcount ischecked to see if it is within a range to be defragmented. The object ischecked to see if the object is owned by the snapshot by comparing anobject ID map of a current and a previous snapshot. If the object isowned and is to be defragmented, then the cloud block in-use map is usedto find free slots and to rewrite the object to comprise data from usedslots and to exclude freed slots. The object header will be updatedaccordingly with new offsets.

Fragmentation may be mitigated. During backup, an object ID map iscreated to contain a bit for each object in use by the snapshot (e.g.,objects storing snapshot data of the snapshot). The mapping metafile(VMAP) is walked to create the object ID map. An object reference mapcan be created to store a count of a number of cloud blocks in use inthat object. If the count is below a threshold, then data of the usedblocks can be rewritten in a new object.

For each primary volume copied to the object store, there is a rootobject having a name starting with a prefix followed by a destinationend point name and UUID. The root object is written during a concludephase. Another copy for the root object is maintained with a unique nameas a defense to eventual consistency, and will have a generation numberappended to the name. A relationship state metafile will be updatedbefore the root object info is updated. The root object has a header,root info, and bookkeeping information. A snapshot info is an objectcontaining snapshot specific information, and is written during aconclude phase of a backup operation. Each object will have its ownunique sequence number, which is generated automatically.

To provide for managing objects within an object store, FIG. 1illustrates an embodiment of a clustered network environment 100 or anetwork storage environment. It may be appreciated, however, that thetechniques, etc. described herein may be implemented within theclustered network environment 100, a non-cluster network environment,and/or a variety of other computing environments, such as a desktopcomputing environment. That is, the instant disclosure, including thescope of the appended claims, is not meant to be limited to the examplesprovided herein. It will be appreciated that where the same or similarcomponents, elements, features, items, modules, etc. are illustrated inlater figures but were previously discussed with regard to priorfigures, that a similar (e.g., redundant) discussion of the same may beomitted when describing the subsequent figures (e.g., for purposes ofsimplicity and ease of understanding).

FIG. 1 is a block diagram illustrating the clustered network environment100 that may implement at least some embodiments of the techniquesand/or systems described herein. The clustered network environment 100comprises data storage systems 102 and 104 that are coupled over acluster fabric 106, such as a computing network embodied as a privateInfiniband, Fibre Channel (FC), or Ethernet network facilitatingcommunication between the data storage systems 102 and 104 (and one ormore modules, component, etc. therein, such as, nodes 116 and 118, forexample). It will be appreciated that while two data storage systems 102and 104 and two nodes 116 and 118 are illustrated in FIG. 1, that anysuitable number of such components is contemplated. In an example, nodes116, 118 comprise storage controllers (e.g., node 116 may comprise aprimary or local storage controller and node 118 may comprise asecondary or remote storage controller) that provide client devices,such as host devices 108, 110, with access to data stored within datastorage devices 128, 130. Similarly, unless specifically providedotherwise herein, the same is true for other modules, elements,features, items, etc. referenced herein and/or illustrated in theaccompanying drawings. That is, a particular number of components,modules, elements, features, items, etc. disclosed herein is not meantto be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, In an embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while In an embodiment a clustered network caninclude data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more host devices 108, 110 which maycomprise, for example, client devices, personal computers (PCs),computing devices used for storage (e.g., storage servers), and othercomputers or peripheral devices (e.g., printers), are coupled to therespective data storage systems 102, 104 by storage network connections112, 114. Network connection may comprise a local area network (LAN) orwide area network (WAN), for example, that utilizes Network AttachedStorage (NAS) protocols, such as a Common Internet File System (CIFS)protocol or a Network File System (NFS) protocol to exchange datapackets, a Storage Area Network (SAN) protocol, such as Small ComputerSystem Interface (SCSI) or Fiber Channel Protocol (FCP), an objectprotocol, such as S3, etc. Illustratively, the host devices 108, 110 maybe general-purpose computers running applications, and may interact withthe data storage systems 102, 104 using a client/server model forexchange of information. That is, the host device may request data fromthe data storage system (e.g., data on a storage device managed by anetwork storage control configured to process I/O commands issued by thehost device for the storage device), and the data storage system mayreturn results of the request to the host device via one or more storagenetwork connections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, cloud storage (e.g., a storage endpoint may bestored within a data cloud), etc., for example. Such a node in theclustered network environment 100 can be a device attached to thenetwork as a connection point, redistribution point or communicationendpoint, for example. A node may be capable of sending, receiving,and/or forwarding information over a network communications channel, andcould comprise any device that meets any or all of these criteria. Oneexample of a node may be a data storage and management server attachedto a network, where the server can comprise a general purpose computeror a computing device particularly configured to operate as a server ina data storage and management system.

In an example, a first cluster of nodes such as the nodes 116, 118(e.g., a first set of storage controllers configured to provide accessto a first storage aggregate comprising a first logical grouping of oneor more storage devices) may be located on a first storage site. Asecond cluster of nodes, not illustrated, may be located at a secondstorage site (e.g., a second set of storage controllers configured toprovide access to a second storage aggregate comprising a second logicalgrouping of one or more storage devices). The first cluster of nodes andthe second cluster of nodes may be configured according to a disasterrecovery configuration where a surviving cluster of nodes providesswitchover access to storage devices of a disaster cluster of nodes inthe event a disaster occurs at a disaster storage site comprising thedisaster cluster of nodes (e.g., the first cluster of nodes providesclient devices with switchover data access to storage devices of thesecond storage aggregate in the event a disaster occurs at the secondstorage site).

As illustrated in the clustered network environment 100, nodes 116, 118can comprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise network modules 120, 122 and disk modules 124, 126. Networkmodules 120, 122 can be configured to allow the nodes 116, 118 (e.g.,network storage controllers) to connect with host devices 108, 110 overthe storage network connections 112, 114, for example, allowing the hostdevices 108, 110 to access data stored in the distributed storagesystem. Further, the network modules 120, 122 can provide connectionswith one or more other components through the cluster fabric 106. Forexample, in FIG. 1, the network module 120 of node 116 can access asecond data storage device by sending a request through the disk module126 of node 118.

Disk modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, disk modules 124, 126 communicate with the data storage devices128, 130 according to the SAN protocol, such as SCSI or FCP, forexample. Thus, as seen from an operating system on nodes 116, 118, thedata storage devices 128, 130 can appear as locally attached to theoperating system. In this manner, different nodes 116, 118, etc. mayaccess data blocks through the operating system, rather than expresslyrequesting abstract files.

It should be appreciated that, while the clustered network environment100 illustrates an equal number of network and disk modules, otherembodiments may comprise a differing number of these modules. Forexample, there may be a plurality of network and disk modulesinterconnected in a cluster that does not have a one-to-onecorrespondence between the network and disk modules. That is, differentnodes can have a different number of network and disk modules, and thesame node can have a different number of network modules than diskmodules.

Further, a host device 108, 110 can be networked with the nodes 116, 118in the cluster, over the storage networking connections 112, 114. As anexample, respective host devices 108, 110 that are networked to acluster may request services (e.g., exchanging of information in theform of data packets) of nodes 116, 118 in the cluster, and the nodes116, 118 can return results of the requested services to the hostdevices 108, 110. In an embodiment, the host devices 108, 110 canexchange information with the network modules 120, 122 residing in thenodes 116, 118 (e.g., network hosts) in the data storage systems 102,104.

In an embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. In an example, a disk array can include alltraditional hard drives, all flash drives, or a combination oftraditional hard drives and flash drives. Volumes can span a portion ofa disk, a collection of disks, or portions of disks, for example, andtypically define an overall logical arrangement of file storage on diskspace in the storage system. In an embodiment a volume can comprisestored data as one or more files that reside in a hierarchical directorystructure within the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the clustered network environment 100, the host devices 108, 110 canutilize the data storage systems 102, 104 to store and retrieve datafrom the volumes 132. In this embodiment, for example, the host device108 can send data packets to the network module 120 in the node 116within data storage system 102. The node 116 can forward the data to thedata storage device 128 using the disk module 124, where the datastorage device 128 comprises volume 132A. In this way, in this example,the host device can access the volume 132A, to store and/or retrievedata, using the data storage system 102 connected by the storage networkconnection 112. Further, in this embodiment, the host device 110 canexchange data with the network module 122 in the node 118 within thedata storage system 104 (e.g., which may be remote from the data storagesystem 102). The node 118 can forward the data to the data storagedevice 130 using the disk module 126, thereby accessing volume 1328associated with the data storage device 130.

It may be appreciated that managing objects within an object store maybe implemented within the clustered network environment 100, such aswhere nodes within the clustered network environment store data asobjects within a remote object store. It may be appreciated thatmanaging objects within an object store may be implemented for and/orbetween any type of computing environment, and may be transferrablebetween physical devices (e.g., node 116, node 118, a desktop computer,a tablet, a laptop, a wearable device, a mobile device, a storagedevice, a server, etc.) and/or a cloud computing environment (e.g.,remote to the clustered network environment 100).

FIG. 2 is an illustrative example of a data storage system 200 (e.g.,102, 104 in FIG. 1), providing further detail of an embodiment ofcomponents that may implement one or more of the techniques and/orsystems described herein. The data storage system 200 comprises a node202 (e.g., nodes 116, 118 in FIG. 1), and a data storage device 234(e.g., data storage devices 128, 130 in FIG. 1). The node 202 may be ageneral purpose computer, for example, or some other computing deviceparticularly configured to operate as a storage server. A host device205 (e.g., 108, 110 in FIG. 1) can be connected to the node 202 over anetwork 216, for example, to provide access to files and/or other datastored on the data storage device 234. In an example, the node 202comprises a storage controller that provides client devices, such as thehost device 205, with access to data stored within data storage device234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other similar media adaptedto store information, including, for example, data (D) and/or parity (P)information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 242. The data storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) optimization technique to optimize areconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202, such as a network storagecontroller, can respond to host device requests to manage data on thedata storage device 234 (e.g., or additional clustered devices) inaccordance with these host device requests. The operating system 208 canoften establish one or more file systems on the data storage system 200,where a file system can include software code and data structures thatimplement a persistent hierarchical namespace of files and directories,for example. As an example, when a new data storage device (not shown)is added to a clustered network system, the operating system 208 isinformed where, in an existing directory tree, new files associated withthe new data storage device are to be stored. This is often referred toas “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and adapters 210,212, 214 for storing related software application code and datastructures. The processors 204 and adapters 210, 212, 214 may, forexample, include processing elements and/or logic circuitry configuredto execute the software code and manipulate the data structures. Theoperating system 208, portions of which are typically resident in thememory 206 and executed by the processing elements, functionallyorganizes the storage system by, among other things, invoking storageoperations in support of a file service implemented by the storagesystem. It will be apparent to those skilled in the art that otherprocessing and memory mechanisms, including various computer readablemedia, may be used for storing and/or executing application instructionspertaining to the techniques described herein. For example, theoperating system can also utilize one or more control files (not shown)to aid in the provisioning of virtual machines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to ahost device 205 over a network 216, which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. The host device 205 (e.g., 108, 110 of FIG. 1) may be ageneral-purpose computer configured to execute applications. Asdescribed above, the host device 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the node 202 to access information requested by the hostdevice 205 (e.g., access data on a storage device managed by a networkstorage controller). The information may be stored on any type ofattached array of writeable media such as magnetic disk drives, flashmemory, and/or any other similar media adapted to store information. Inthe example data storage system 200, the information can be stored indata blocks on the disks 224, 226, 228. The storage adapter 214 caninclude input/output (I/O) interface circuitry that couples to the disksover an I/O interconnect arrangement, such as a storage area network(SAN) protocol (e.g., Small Computer System Interface (SCSI), iSCSI,hyperSCSI, Fiber Channel Protocol (FCP)). The information is retrievedby the storage adapter 214 and, if necessary, processed by the one ormore processors 204 (or the storage adapter 214 itself) prior to beingforwarded over the system bus 242 to the network adapter 210 (and/or thecluster access adapter 212 if sending to another node in the cluster)where the information is formatted into a data packet and returned tothe host device 205 over the network 216 (and/or returned to anothernode attached to the cluster over the cluster fabric 215).

In an embodiment, storage of information on disk arrays 218, 220, 222can be implemented as one or more storage volumes 230, 232 that arecomprised of a cluster of disks 224, 226, 228 defining an overalllogical arrangement of disk space. The disks 224, 226, 228 that compriseone or more volumes are typically organized as one or more groups ofRAIDs. As an example, volume 230 comprises an aggregate of disk arrays218 and 220, which comprise the cluster of disks 224 and 226.

In an embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, whereas directories may be implemented asspecially formatted files in which information about other files anddirectories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume corresponds to at least a portion of physical storagedevices whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalstorage device locations, such as some available space from each of thedisks 224, 226, and/or 228. It will be appreciated that since a virtualvolume is not “tied” to any one particular storage device, a virtualvolume can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, Qtrees 235, and files 240. Among otherthings, these features, but more particularly LUNS, allow the disparatememory locations within which data is stored to be identified, forexample, and grouped as data storage unit. As such, the LUNs 238 may becharacterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In an embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumesstored on a data storage device, a target address on the data storagedevice can be used to identify one or more LUNs 238. Thus, for example,when the node 202 connects to a volume 230, 232 through the storageadapter 214, a connection between the node 202 and the one or more LUNs238 underlying the volume is created.

In an embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the one or more LUNs 238.

It may be appreciated that managing objects within an object store maybe implemented for the data storage system 200. It may be appreciatedthat managing objects within an object store may be implemented forand/or between any type of computing environment, and may betransferrable between physical devices (e.g., node 202, host device 205,a desktop computer, a tablet, a laptop, a wearable device, a mobiledevice, a storage device, a server, etc.) and/or a cloud computingenvironment (e.g., remote to the node 202 and/or the host device 205).

One embodiment of managing objects within an object store is illustratedby an exemplary method 300 of FIG. 3 and further described inconjunction with system 400 of FIG. 4. A computing device may comprise anode, a storage controller, a storage service, an on-premises computingdevice, a storage virtual machine, or any other hardware or software(e.g., software as a service). The computing device may store datawithin storage devices (primary storage) managed by the computingdevice. The computing device may provide client devices with access tothe data, such as by processing read and write operations from theclient devices. The computing device may create snapshots of the data,such as a snapshot of a file system of a volume accessible to the clientdevices through the computing device.

The computing device may be configured to communicate with an objectstore 406 over a network. The object store 406 may comprise a cloudcomputing environment remote to the computing device, and is accessibleto the computing device over a network. The object store 406 may providescalable cost effective storage for the computing device and/or othercomputing devices. Accordingly, various computing devices and/orapplications may store data within the object store 406 through objects.For example, a first application 402 executed on a computing device maystore data within objects stored within the object store 406. A secondapplication 404 executing on a computing device (e.g., the same ordifferent computing device than the computing device executing the firstapplication) may store data within objects stored within the objectstore.

At 302, an object 408 is maintained within the object store 406, asillustrated by FIG. 4. The object 408 comprises a plurality of slots 414for storing user data. The object 408 may comprise any number of slots,such as 1024 slots or any other number of slots. In particular, a slotis used to store a unit of data accessible to applications hosted byremote computing devices, such as the first application 402 and thesecond application 404. The object 408 comprises an object header 410used to store metadata 412 for each slot. The object header 410 has astatic array of slot context comprising information used to access theuser data within the slots. Each slot can represent any length oflogical data (e.g., a slot is a base unit of data of the object filesystem of the object store). Since data blocks for metadata arenormalized, a slot can represent any length of logical data. Data withinthe slots can be compressed into compression groups, and a slot willcomprise enough information for how to decompress and return data of theslot.

The slot context may comprise information relating to a type ofcompression used for compressing data within the object 408 (if anycompression is used), a start offset of a slot, a logical data length, acompressed data length, etc. The slot context may be used to accesscompressed data stored within the object 408. The object header 410 mayhave a size that is aligned with a start of the plurality of slots 414,such as having a 4 kb alignment based upon each slot having a logicallength of 4 kb. It may be appreciated that slots may have any length.The object header 410 comprises various information, such as a versionidentifier, a header checksum, a length of the object 408, a slotcontext, and/or other information used to access and manage datapopulated into the slots of the object 408. The slot context comprisesvarious information about the slots, such as a compression type of aslot (e.g., a type of compression used to compress data of slots into acompression group or an indicator that the slot does not comprisecompressed data), a start offset of the slot within the object 408(e.g., a slot identifier multiplied by a slot size, such as 4 kb), alogical data length of the slot (e.g., 4 kb), a compressed length (e.g.,0 if uncompressed), an index of the slot within a compression group ofmultiple slots (e.g., 0 if uncompressed), a logical data checksum, etc.

The object 408 may comprise a logical representation of data stored intothe object 408 by a remote computing device. The object 408 may compriseany types of data, such as a file, user data, a directory, a read onlysnapshot of a file system hosted by the remote computing device, etc.Each object within the object store 406 is assigned a unique sequenceidentifier for uniquely identifying each object.

At 304, a first rule is enforced for the object 408. The first rule mayspecify that in-use slots of the object 408 are non-modifiable. Anin-use slot is a slot comprising data still used and/or referenced bythe remote computing device. The first rule may specify that unusedslots are modifiable. An unused slot is a slot comprising data that isno longer used or referenced by the remote computing device, such asfreed data unique to a snapshot that has been deleted by the remotecomputing device and thus is no longer used or referenced by the remotecomputing device.

At 306, metadata 412, of additional information for a slot within theobject 408, is attached to the object header 410. The additionalinformation may comprise analytics (e.g., read/write statistics ofaccess to the object 408), virus scan information, development testingdata, and/or a variety of other information that can be generated forthe object 408 and the data stored therein. In an example, theadditional data is generated by a cloud service or application executingwithin the object store 406. This will offload processing and resourceutilization that would otherwise be used by the remote computing device(primary storage system) to perform such analytics and processing.

When the metadata 412 is attached to the object 408, the user datawithin the slots 414 is retained in an unmodified state based uponenforcement of the first rule. That is, the first rule specifies thatin-use data within the slots cannot be modified. Thus, when the metadata412 is attached to the object 408, slots comprising in-use data are notmodified.

When the metadata 412 is attached to the object 408, the meaning andaccessibility of the in-use data within the slots 414 is not changed.For example, the first application 402 may have original had access 416to user data within the slots 414. Once the metadata 412 is attached tothe object 408, the first application 402 still retains access 416 tothe user data within the slots 414. The meaning and accessible that thefirst application has to the object 408 is not changed by the metadata412 being attached to the object 408, and thus the access 416 does notadditionally provide the first application 402 with access to themetadata 412 comprising the additional information, such as theanalytics. The second application 404 may have created the metadata 412,requested that the metadata 412 be created (e.g., analytics created by acloud service invoked by the second application 404), or otherwise havesome association with the metadata 412. Accordingly, the secondapplication 404 has access 418 to the user data within the slots 414that the second application 404 always had access to and has access tothe metadata 412 to which the second application 404 is associated.

In an embodiment, a second rule is enforced for objects within theobject store 406. The second rule specifies that read operations are tobe directed to a same version of the object 408. That is, a plurality ofversion of the object 408 may be maintained within the object store 406.For example, the object 408 may be incrementally updated over time.Because in-use data of the object 408 is not to be modified per thefirst rule, new versions of the object are created for each incrementalupdate to store new data so that existing in-use data of the object 408is not overwritten or modified. In this way, a new version of the object408 is created to comprise new user data that would otherwise overwritecurrent user data within a current version of the object 408 inviolation of the first rule.

In an example of enforcing the second rule, a first read operation isperformed to read the object header 410 to obtain slot information of aslot from which data is to be read. A second read operation is performedto read the data from the slot as identified by the slot information. Atimestamp comparison is performed to compare timestamp data returned forthe first read operation and the second read operation to determinewhether the first read operation and the second read operation wereexecuted upon the same version of the object 408 based upon whether thetimestamp data matches (e.g., a timestamp may be associated with eachobject version). If the timestamp data does not match, then the firstread operation and the second read operation were executed upondifferent versions of the object 408, and thus the read operations areretried or failed.

One embodiment of managing objects within an object store is illustratedby an exemplary method 500 of FIG. 5 and further described inconjunction with system 600 of FIG. 6. A computing device 610 maycomprise a node, a storage controller, a storage service, an on-premisescomputing device, a storage virtual machine, or any other hardware orsoftware (e.g., software as a service). The computing device 610 maystore data within storage devices (primary storage) managed by thecomputing device 610. The computing device 610 may provide clientdevices with access to the data, such as by processing read and writeoperations from the client devices. The computing device 610 may createsnapshots of the data, such as a snapshot of a file system of a volumeaccessible to the client devices through the computing device 610.

The computing device 610 may be configured to communicate with an objectstore 618 over a network. The object store 618 may comprise a cloudcomputing environment remote to the computing device 610, and isaccessible to the computing device 610 over a network. The object store618 may provide scalable cost effective storage for the computing device610 and/or other computing devices. Accordingly, various computingdevices and/or applications may store data within the object store 618through objects.

In an example, the computing device 610 may create a first snapshot ofdata maintained by the computing device 610 within primary storage. Thefirst snapshot may be copied to the object store 618 as a first object602 comprising slots within which data of the first snapshot are stored.The computing device 610 may create a second snapshot of data maintainedby the computing device 610 within the primary storage. The secondsnapshot may be copied to the object store 618 as a second object 604comprising slots within which data of the second snapshot are stored.The computing device 610 may create a third snapshot of data maintainedby the computing device 610 within the primary storage. The thirdsnapshot may be copied to the object store 618 as a third object 606comprising slots within which data of the third snapshot are stored. Inthis way, the computing device 610 may copy snapshots to the objectstore 618, such that copied snapshot data is stored within objects ofthe object store 618.

When objects are created and stored to the object store 618, bitmaps 616are created to describe the objects. In an embodiment, a bitmap for thefirst object 602 may specify that the first object 602 comprises data ofthe first snapshot and/or any other snapshots for which the first object602 is storing data. A bitmap for the second object 604 may specify thatthe second object 604 comprises data of the second snapshot and/or anyother snapshots for which the second object 604 is storing data. Abitmap for the third object 606 may specify that the third object 606comprises data of the third snapshot and/or any other snapshots forwhich the third object 606 is storing data. In an embodiment, instead ofcreating and maintaining a bitmap per object, bitmaps may be created foreach snapshot. Thus, a bitmap for the first snapshot may specify whichobjects store data of the first snapshot, such as the first object 602and/or any other objects storing data of the first snapshot. A bitmapfor the second snapshot may specify which objects store data of thesecond snapshot, such as the second object 604 and/or any other objectsstoring data of the second snapshot. A bitmap for the third snapshot mayspecify which objects store data of the third snapshot, such as thethird object 606 and/or any other objects storing data of the thirdsnapshot. In this way, each snapshot may be a snapshot of a file systemmaintained by the computing device 610, and each snapshot is associatedwith a bitmap identifying objects within the object store 618 thatcorrespond to (e.g., comprise data of) a particular snapshot. In anembodiment, a single bitmap may be maintained for a single snapshot ormultiple snapshots or may be maintained for a single object or multipleobjects.

At 502, a determination may be made that the computing device 610deleted 612 the first snapshot. At 504, the bitmaps 616 are evaluated todetermine whether there are any objects that are unique to the deleted612 first snapshot. For example, the first object 602 and a fourthobject may comprise data only of the deleted 612 first snapshot and noother data corresponding to other snapshots or data maintained by thecomputing device 610. Accordingly, any objects that are unique to thedeleted 612 first snapshot, such as the first object 602 and the fourthobject, are freed from storage of the object store 618, at 508. Anyobjects that are not uniquely associated with the deleted 612 firstsnapshot (e.g., the second object 604 and the third object 606 do notcomprise data of the first snapshot and a fifth object comprises data ofthe first snapshot but also data of another snapshot and thus is notunique to only to the first snapshot), are retained within the objectstore 618. In this way, a garbage collection operation 614 is performed,such as by a cloud service hosted within the object store 618, to freeobjects from storage of the object store 618 based upon the objectsuniquely corresponding to deleted snapshots maintained by the computingdevice 610.

One embodiment of managing objects within an object store is illustratedby an exemplary method 700 of FIG. 7 and further described inconjunction with system 800 of FIG. 8. A computing device 810 maycomprise a node, a storage controller, a storage service, an on-premisescomputing device, a storage virtual machine, or any other hardware orsoftware (e.g., software as a service). The computing device 810 maystore data within storage devices (primary storage) managed by thecomputing device 810. The computing device 810 may provide clientdevices with access to the data, such as by processing read and writeoperations from the client devices. The computing device 810 may createsnapshots of the data, such as a snapshot of a file system of a volumeaccessible to the client devices through the computing device 810.

The computing device 810 may be configured to communicate with an objectstore 808 over a network. The object store 808 may comprise a cloudcomputing environment remote to the computing device 810, and isaccessible to the computing device 810 over a network. The object store808 may provide scalable cost effective storage for the computing device810 and/or other computing devices. Accordingly, various computingdevices and/or applications may store data within the object store 808through objects, such as a first object 802, a second object 804, athird object 806, and/or other objects, at 702.

An object may correspond to data maintained by the computing device 810.For example, the first object 802 comprises slots into which snapshotdata, of a snapshot created by the computing device 810 of a file systemmaintained by the computing device 810, and/or other data is stored.Over time, the computing device 810 may no longer reference or usecertain data that was stored into the first object 802. For example, thesnapshot may be deleted by the computing device 810. Thus, some of theslots of the first object 802 may be freed slots because those slotscomprise data unique to the snapshot that was deleted. The freed slotsthus comprise freed data no longer used or referenced by the computingdevice 810. However, some of the slots of the first object 802 may bein-use slots that comprise in-use data that is still used or referencedby the computing device 810. An object header of the first object 802may comprise metadata that specifies the locations of the data, such asin-use data, within the first object 802, such as which slots comprisecertain data.

Accordingly, defragmentation 812 may be performed for objects within theobject store 808 in order to reduce storage utilization otherwise wastedin store freed data within freed slots because the freed data is nolonger used or referenced by the computing device 810. At 704, adetermination is made that an object is a fragmented object because thefragmented object comprise freed slots from which data was freed (e.g.,the first object 802 comprising freed slots storing data of the snapshotthat was deleted by the computing device 810) and in-use slots of in-usedata (e.g., the first object 802 comprises in-use slots storing datastill used or referenced by the computing device 810). At 706, theobject may be compacted to retain the in-use data and exclude the freeddata. The object may be compacted to create a rewritten object. Therewritten object comprises the in-use data stored within slots of therewritten object. The rewritten object excludes the freed data no longerused or referenced by the computing device 810. Because the location ofthe in-use data may be different in the rewritten object than the object(e.g., the in-use data may be stored in different slots), the metadatawithin the object header of the rewritten object is updated with the newlocations of the in-use data within the rewritten object.

Still another embodiment involves a computer-readable medium 900comprising processor-executable instructions configured to implement oneor more of the techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 9, wherein the implementationcomprises a computer-readable medium 908, such as a compactdisc-recordable (CD-R), a digital versatile disc-recordable (DVD-R),flash drive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 906. This computer-readable data 906, such asbinary data comprising at least one of a zero or a one, in turncomprises a processor-executable computer instructions 904 configured tooperate according to one or more of the principles set forth herein. Insome embodiments, the processor-executable computer instructions 904 areconfigured to perform a method 902, such as at least some of theexemplary method 300 of FIG. 3, at least some of the exemplary method500 of FIG. 5, and/or at least some of the exemplary method 700 of FIG.7, for example. In some embodiments, the processor-executable computerinstructions 904 are configured to implement a system, such as at leastsome of the exemplary system 400 of FIG. 4, at least some of theexemplary system 600 of FIG. 6, and/or at least some of the exemplarysystem 800 of FIG. 8, for example. Many such computer-readable media arecontemplated to operate in accordance with the techniques presentedherein.

FIG. 10 is a diagram illustrating an example operating environment 1000in which an embodiment of the techniques described herein may beimplemented. In one example, the techniques described herein may beimplemented within a client device 1028, such as a laptop, tablet,personal computer, mobile device, wearable device, etc. In anotherexample, the techniques described herein may be implemented within astorage controller 1030, such as a node configured to manage the storageand access to data on behalf of the client device 1028 and/or otherclient devices. In another example, the techniques described herein maybe implemented within a distributed computing platform 1002 such as acloud computing environment (e.g., a cloud storage environment, amulti-tenant platform, etc.) configured to manage the storage and accessto data on behalf of the client device 1028 and/or other client devices.

In yet another example, at least some of the techniques described hereinare implemented across one or more of the client device 1028, thestorage controller 1030, and the distributed computing platform 1002.For example, the client device 1028 may transmit operations, such asdata operations to read data and write data and metadata operations(e.g., a create file operation, a rename directory operation, a resizeoperation, a set attribute operation, etc.), over a network 1026 to thestorage controller 1030 for implementation by the storage controller1030 upon storage. The storage controller 1030 may store data associatedwith the operations within volumes or other data objects/structureshosted within locally attached storage, remote storage hosted by othercomputing devices accessible over the network 1026, storage provided bythe distributed computing platform 1002, etc. The storage controller1030 may replicate the data and/or the operations to other computingdevices so that one or more replicas, such as a destination storagevolume that is maintained as a replica of a source storage volume, aremaintained. Such replicas can be used for disaster recovery andfailover.

The storage controller 1030 may store the data or a portion thereofwithin storage hosted by the distributed computing platform 1002 bytransmitting the data to the distributed computing platform 1002. In oneexample, the storage controller 1030 may locally store frequentlyaccessed data within locally attached storage. Less frequently accesseddata may be transmitted to the distributed computing platform 1002 forstorage within a data storage tier 1008. The data storage tier 1008 maystore data within a service data store 1020, and may store clientspecific data within client data stores assigned to such clients such asa client (1) data store 1022 used to store data of a client (1) and aclient (N) data store 1024 used to store data of a client (N). The datastores may be physical storage devices or may be defined as logicalstorage, such as a virtual volume, LUNs, or other logical organizationsof data that can be defined across one or more physical storage devices.In another example, the storage controller 1030 transmits and stores allclient data to the distributed computing platform 1002. In yet anotherexample, the client device 1028 transmits and stores the data directlyto the distributed computing platform 1002 without the use of thestorage controller 1030.

The management of storage and access to data can be performed by one ormore storage virtual machines (SMVs) or other storage applications thatprovide software as a service (SaaS) such as storage software services.In one example, an SVM may be hosted within the client device 1028,within the storage controller 1030, or within the distributed computingplatform 1002 such as by the application server tier 1006. In anotherexample, one or more SVMs may be hosted across one or more of the clientdevice 1028, the storage controller 1030, and the distributed computingplatform 1002.

In one example of the distributed computing platform 1002, one or moreSVMs may be hosted by the application server tier 1006. For example, aserver (1) 1016 is configured to host SVMs used to execute applicationssuch as storage applications that manage the storage of data of theclient (1) within the client (1) data store 1022. Thus, an SVM executingon the server (1) 1016 may receive data and/or operations from theclient device 1028 and/or the storage controller 1030 over the network1026. The SVM executes a storage application to process the operationsand/or store the data within the client (1) data store 1022. The SVM maytransmit a response back to the client device 1028 and/or the storagecontroller 1030 over the network 1026, such as a success message or anerror message. In this way, the application server tier 1006 may hostSVMs, services, and/or other storage applications using the server (1)1016, the server (N) 1018, etc.

A user interface tier 1004 of the distributed computing platform 1002may provide the client device 1028 and/or the storage controller 1030with access to user interfaces associated with the storage and access ofdata and/or other services provided by the distributed computingplatform 1002. In an example, a service user interface 1010 may beaccessible from the distributed computing platform 1002 for accessingservices subscribed to by clients and/or storage controllers, such asdata replication services, application hosting services, data securityservices, human resource services, warehouse tracking services,accounting services, etc. For example, client user interfaces may beprovided to corresponding clients, such as a client (1) user interface1012, a client (N) user interface 1014, etc. The client (1) can accessvarious services and resources subscribed to by the client (1) throughthe client (1) user interface 1012, such as access to a web service, adevelopment environment, a human resource application, a warehousetracking application, and/or other services and resources provided bythe application server tier 1006, which may use data stored within thedata storage tier 1008.

The client device 1028 and/or the storage controller 1030 may subscribeto certain types and amounts of services and resources provided by thedistributed computing platform 1002. For example, the client device 1028may establish a subscription to have access to three virtual machines, acertain amount of storage, a certain type/amount of data redundancy, acertain type/amount of data security, certain service level agreements(SLAs) and service level objectives (SLOs), latency guarantees,bandwidth guarantees, access to execute or host certain applications,etc. Similarly, the storage controller 1030 can establish a subscriptionto have access to certain services and resources of the distributedcomputing platform 1002.

As shown, a variety of clients, such as the client device 1028 and thestorage controller 1030, incorporating and/or incorporated into avariety of computing devices may communicate with the distributedcomputing platform 1002 through one or more networks, such as thenetwork 1026. For example, a client may incorporate and/or beincorporated into a client application (e.g., software) implemented atleast in part by one or more of the computing devices.

Examples of suitable computing devices include personal computers,server computers, desktop computers, nodes, storage servers, storagecontrollers, laptop computers, notebook computers, tablet computers orpersonal digital assistants (PDAs), smart phones, cell phones, andconsumer electronic devices incorporating one or more computing devicecomponents, such as one or more electronic processors, microprocessors,central processing units (CPU), or controllers. Examples of suitablenetworks include networks utilizing wired and/or wireless communicationtechnologies and networks operating in accordance with any suitablenetworking and/or communication protocol (e.g., the Internet). In usecases involving the delivery of customer support services, the computingdevices noted represent the endpoint of the customer support deliveryprocess, i.e., the consumer's device.

The distributed computing platform 1002, such as a multi-tenant businessdata processing platform or cloud computing environment, may includemultiple processing tiers, including the user interface tier 1004, theapplication server tier 1006, and a data storage tier 1008. The userinterface tier 1004 may maintain multiple user interfaces, includinggraphical user interfaces and/or web-based interfaces. The userinterfaces may include the service user interface 1010 for a service toprovide access to applications and data for a client (e.g., a “tenant”)of the service, as well as one or more user interfaces that have beenspecialized/customized in accordance with user specific requirements,which may be accessed via one or more APIs.

The service user interface 1010 may include components enabling a tenantto administer the tenant's participation in the functions andcapabilities provided by the distributed computing platform 1002, suchas accessing data, causing execution of specific data processingoperations, etc. Each processing tier may be implemented with a set ofcomputers, virtualized computing environments such as a storage virtualmachine or storage virtual server, and/or computer components includingcomputer servers and processors, and may perform various functions,methods, processes, or operations as determined by the execution of asoftware application or set of instructions.

The data storage tier 1008 may include one or more data stores, whichmay include the service data store 1020 and one or more client datastores. Each client data store may contain tenant-specific data that isused as part of providing a range of tenant-specific business andstorage services or functions, including but not limited to ERP, CRM,eCommerce, Human Resources management, payroll, storage services, etc.Data stores may be implemented with any suitable data storagetechnology, including structured query language (SQL) based relationaldatabase management systems (RDBMS), file systems hosted by operatingsystems, object storage, etc.

In accordance with one embodiment of the invention, the distributedcomputing platform 1002 may be a multi-tenant and service platformoperated by an entity in order to provide multiple tenants with a set ofbusiness related applications, data storage, and functionality. Theseapplications and functionality may include ones that a business uses tomanage various aspects of its operations. For example, the applicationsand functionality may include providing web-based access to businessinformation systems, thereby allowing a user with a browser and anInternet or intranet connection to view, enter, process, or modifycertain types of business information or any other type of information.

In an embodiment, the described methods and/or their equivalents may beimplemented with computer executable instructions. Thus, In anembodiment, a non-transitory computer readable/storage medium isconfigured with stored computer executable instructions of analgorithm/executable application that when executed by a machine(s)cause the machine(s) (and/or associated components) to perform themethod. Example machines include but are not limited to a processor, acomputer, a server operating in a cloud computing system, a serverconfigured in a Software as a Service (SaaS) architecture, a smartphone, and so on). In an embodiment, a computing device is implementedwith one or more executable algorithms that are configured to performany of the disclosed methods.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), electrically erasable programmable read-only memory(EEPROM) and/or flash memory, compact disk read only memory (CD-ROM)s,CD-Rs, compact disk re-writeable (CD-RW)s, DVDs, cassettes, magnetictape, magnetic disk storage, optical or non-optical data storage devicesand/or any other medium which can be used to store data.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: maintaining an object,comprising a plurality of slots, within an object store, wherein eachslot is used to store a unit of data accessible to applications hostedby remote computing devices, wherein the object comprises an objectheader used to store metadata for each slot, wherein the object is usedto store data of a snapshot of a file system hosted by a remotecomputing device; determining that the snapshot was deleted by theremote computing device; evaluating bitmaps describing objects withinthe object store that are related to snapshots of the file system todetermine that the object is unique to the deleted snapshot; and freeingthe object from storage within the object store.
 2. The method of claim1, wherein a second object is identified as being unique to the deletedsnapshot and the method comprising: freeing the second object fromstorage within the object store.
 3. The method of claim 1, comprising:evaluating the bitmaps to determine that a second object is associatedwith the deleted snapshot and a second snapshot.
 4. The method of claim3, comprising: retaining the second object within storage of the objectstore.
 5. The method of claim 1, wherein each snapshot of the filesystem is associated with a bitmap identifying objects within the objectstore that correspond to a snapshot.
 6. The method of claim 1, wherein acloud service hosted within the object store performs a garbagecollection operation to free objects from storage within the objectstore based upon the objects uniquely corresponding to deletedsnapshots.
 7. The method of claim 1, wherein the object comprises a readonly snapshot of the file system.
 8. The method of claim 7, wherein aplurality of objects, corresponding to read only snapshots of the filesystem, are stored within the object store.
 9. The method of claim 8,wherein each object is assigned a unique sequence identifier.
 10. Anon-transitory machine readable medium comprising instructions forperforming a method, which when executed by a machine, causes themachine to: maintain an object, comprising a plurality of slots, withinan object store, wherein each slot is used to store a unit of dataaccessible to applications hosted by remote computing devices, whereinthe object comprises an object header used to store metadata for eachslot, wherein the object is used to store data of a snapshot of a filesystem hosted by a remote computing device; determine that the snapshotwas deleted by the remote computing device; evaluate bitmaps describingobjects within the object store that are related to snapshots of thefile system to determine that the object is unique to the deletedsnapshot; and free the object from storage within the object store. 11.The non-transitory machine readable medium of claim 10, wherein a secondobject is identified as being unique to the deleted snapshot, andwherein the instructions cause the machine to: free the second objectfrom storage within the object store.
 12. The non-transitory machinereadable medium of claim 10, wherein the instructions cause the machineto: evaluate the bitmaps to determine that a second object is associatedwith the deleted snapshot and a second snapshot.
 13. The non-transitorymachine readable medium of claim 12, wherein the instructions cause themachine to: retain the second object within storage of the object store.14. The non-transitory machine readable medium of claim 10, wherein eachsnapshot of the file system is associated with a bitmap identifyingobjects within the object store that correspond to a snapshot.
 15. Thenon-transitory machine readable medium of claim 10, wherein a cloudservice hosted within the object store performs a garbage collectionoperation to free objects from storage within the object store basedupon the objects uniquely corresponding to deleted snapshots.
 16. Acomputing device comprising: a memory comprising machine executable codefor performing a method; and a processor coupled to the memory, theprocessor configured to execute the machine executable code to cause theprocessor to: maintain an object, comprising a plurality of slots,within an object store, wherein each slot is used to store a unit ofdata accessible to applications hosted by remote computing devices,wherein the object comprises an object header used to store metadata foreach slot, wherein the object is used to store data of a snapshot of afile system hosted by a remote computing device; determine that thesnapshot was deleted by the remote computing device; evaluate bitmapsdescribing objects within the object store that are related to snapshotsof the file system to determine that the object is unique to the deletedsnapshot; and free the object from storage within the object store. 17.The computing device of claim 16, wherein a second object is identifiedas being unique to the deleted snapshot, and wherein the machineexecutable code causes the processor to: free the second object fromstorage within the object store.
 18. The computing device of claim 16,wherein the machine executable code causes the processor to: evaluatethe bitmaps to determine that a second object is associated with thedeleted snapshot and a second snapshot.
 19. The computing device ofclaim 18, wherein the machine executable code causes the processor to:retain the second object within storage of the object store.
 20. Thecomputing device of claim 16, wherein each snapshot of the file systemis associated with a bitmap identifying objects within the object storethat correspond to a snapshot.